Weird Stems with beam::align-with-broken-parts and beam::slope-like-broken-parts

[Thomas Morley]

Hi,

the following code returns missing Stems.
(A larger example would show not only missing but also all sorts of weird Stems.
see:
http://lists.gnu.org/archive/html/lilypond-user/2013-06/msg00334.html
)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\version "2.17.20"

\paper {
        %indent = 0
        ragged-right = ##t
}

\layout {
        \override Beam #'breakable = ##t
        \override Beam #'positions = #beam::align-with-broken-parts
        %\override Beam.positions = #beam::slope-like-broken-parts
}

\relative c' {
  c2.. c''8[ \break
  a,] r c2.
}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

The terminal returns:
warning: weird stem size, check for narrow beams
  c2..
       c''8[ \break
warning: Not drawing a box with negative dimension, 0.13 by -0.24.

Some observations:
1)
The bug is triggered if only _one_ beamed Stem is present before line-break.
Two or more beamed Stems make the bug disappear:

\relative c' {
  c2. c''8[ c \break
  a,] r c2.
}

works always nice.

2)
The relevant regtest beam-broken-classic.ly doesn't test this case
(i.e. only one beamed Stem before line-break)

3)
When uncommenting `indent = 0' no warning is printed to the terminal,
though the printed output is still worse.

4)
With \override Beam.positions = #beam::slope-like-broken-parts no
terminal-output appears, though the pdf is bad, too.

5)
The bug is present in 2.16.2, too.



Cheers,
  Harm